Elsevier

Clinical Biomechanics

Volume 26, Issue 1, January 2011, Pages 1-12
Clinical Biomechanics

Review
Mechanisms of rotator cuff tendinopathy: Intrinsic, extrinsic, or both?

https://doi.org/10.1016/j.clinbiomech.2010.08.001Get rights and content

Abstract

The etiology of rotator cuff tendinopathy is multi-factorial, and has been attributed to both extrinsic and intrinsic mechanisms. Extrinsic factors that encroach upon the subacromial space and contribute to bursal side compression of the rotator cuff tendons include anatomical variants of the acromion, alterations in scapular or humeral kinematics, postural abnormalities, rotator cuff and scapular muscle performance deficits, and decreased extensibility of pectoralis minor or posterior shoulder. A unique extrinsic mechanism, internal impingement, is attributed to compression of the posterior articular surface of the tendons between the humeral head and glenoid and is not related to subacromial space narrowing. Intrinsic factors that contribute to rotator cuff tendon degradation with tensile/shear overload include alterations in biology, mechanical properties, morphology, and vascularity. The varied nature of these mechanisms indicates that rotator cuff tendinopathy is not a homogenous entity, and thus may require different treatment interventions. Treatment aimed at addressing mechanistic factors appears to be beneficial for patients with rotator cuff tendinopathy, however, not for all patients. Classification of rotator cuff tendinopathy into subgroups based on underlying mechanism may improve treatment outcomes.

Section snippets

Extrinsic mechanisms of rotator cuff tendinopathy

Extrinsic mechanisms of RC tendinopathy that result in bursal-sided RC tendon compression due to narrowing of the subacromial space include anatomical factors, biomechanical factors, or a combination. The subacromial space is the interval between the coracoacromial arch, anterior acromion and the humeral head (Neer and Poppen, 1987). The acromiohumeral distance (AHD), a linear measure between the acromion and the humeral head used to quantify the subacromial space, has been studied in patients

Extrinsic mechanisms for the subgroup of internal impingement

A unique subset of RC tendinopathy with an extrinsic mechanism is internal impingement. Patients with internal impingement tend to present with pain located in the posterior and superior aspects of the shoulder typically while the arm is in abduction and external rotation of the late cocking phase of throwing (Jobe, 1995, Kvitne and Jobe, 1993). In this position, the articular aspect of the RC tendons becomes mechanically impinged between the posterior superior glenoid rim and the humeral head.

Intrinsic mechanisms of rotator cuff tendinopathy

There is a growing body of evidence to support an intrinsic mechanism. Intrinsic mechanisms of RC tendinopathy influence tendon morphology and performance. Intrinsic factors of RC tendinopathy result in tendon degradation due to the natural process of aging (Iannotti et al., 1991, Milgrom et al., 1995, Sher et al., 1995, Tempelhof et al., 1999), poor vascularity (Biberthaler et al., 2003, Brooks et al., 1992, Fukuda et al., 1990, Goodmurphy et al., 2003, Rathbun and Macnab, 1970, Rudzki et al.,

Subgroups of patients with tendinopathy based on mechanism

Subgroups of RC tendinopathy may exist, based on intrinsic and extrinsic mechanism that may serve to facilitate treatment decision-making for patients with RC tendinopathy. In a cadaver study, bursal-sided tendon degeneration with partial thickness tears were always associated with attritional lesions on the coracoacromial ligament and anterior third of the acromion (Ozaki et al., 1988); however, this was not true of articular-sided RC pathology in which the undersurface of the acromion was

Conclusion

RC tendinopathy is a common disorder that poses challenges for effective treatment. Evidence suggests that extrinsic, intrinsic, and combinations of biomechanical mechanisms play a role. Intrinsic mechanisms, such as RC tendon mechanical properties, composition, and vascularity, and extrinsic mechanisms, such as alterations in scapular and glenohumeral kinematics that contribute to either internal and external impingement, appear to be particularly significant factors of RC tendinopathy.

Acknowledgements

This work was partially funded by the Foundation for Physical Therapy and the National Athletic Trainers' Association Research and Education Foundation.

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